Short-Wave Infrared Emissions from Te sup(4+)-Ln sup(3+) (Ln: Er, Yb)-Codoped Cs sub(2)NaInCl sub(6) Double Perovskites

Abstract

A Cs sub(2)NaInCl sub(6) double perovskite is environmentally benign, and its wide band gap (approx. 5.1 eV) makes it photoinactive and photostable in the ultraviolet, visible, and short-wave infrared (SWIR) regions. Interestingly, the octahedrally coordinated In sup(3+) lattice site is suitable for doping lanthanide ions like Er sup(3+) and Yb sup(3+), which can emit SWIR radiation at 1540 nm (0.805 eV) and 994 nm (1.247 eV), respectively. But the optical excitation of lanthanides is Laporte forbidden, and the host requires excitation energy greater than 5.1 eV. The large Stokes shift for the excitation and SWIR emission reduces the power conversion efficiency. Here, we codoped Te sup(4+) with Er sup(3+) or Yb sup(3+) into Cs sub(2)NaInCl sub(6). Te sup(4+) absorbs at the sub-band-gap level at around 3.1 eV (400 nm) because of 5s sup(2) → 5s sup(1)5p sup(1) electronic transitions. Then, the excited Te sup(4+) transfers its energy nonradiatively to an Er sup(3+) or Yb sup(3+) codopant. The de-excitation of Er sup(3+) or Yb sup(3+) through f-f electronic transitions emits SWIR radiation at 1540 and 994 nm, respectively, along with weak visible-light emissions. Temperature (8-300 K) dependent photoluminescence excitation, emission, and lifetime measurements reveal the mechanism of these energy transfer processes. Finally, we fabricated a simple phosphor-converted light-emitting diode (pc-LED) emitting SWIR radiation.